[unreadable] Peptides produced by nonribosomal peptide synthetases (NRPSs) function therapeutically as antibiotics, antitumor agents, and immuno-suppressants. This activity has heightened interest in studying the modular enzyme parts responsible for their synthesis, with the long-term goal of interchanging modules to affect the combinatorial biosynthesis of libraries of new therapeutic agents. This proposal is focused on determining the origin of the epimerase activity in the NRPS from Pseudomas syringae that produces the phytotoxin syringomycin. Specifically, syringomycin contains multiple D-amino acid residues, but the syringomycin NRPS, like all other NRPSs of Pseudomonas origin, does not contain the 50 kD epimerase domains typically found in the NPRS assembly lines of gram positive bacteria. We propose to determine which one of the other three domains that are present (adenylation, thioesterification, and condensation) contains novel dual activity, thereby functioning as an effective epimerization domain, as a prelude to collecting domains that insert and elongate D- vs L-amino acid residues. [unreadable] [unreadable]